1. Technical Field
The present invention relates to an on-vehicle charging apparatus for charging a battery by a generator (i.e., alternator) mounted in vehicles such as passenger cars and trucks and a control apparatus for controlling the generated state of the on-vehicle generator.
2. Related Art
Most vehicles are provided with AC (alternating current) generators (i.e., alternators) driven by on-vehicle engines to generate electric power. The operation of such a generator is controlled by a control apparatus called an IC regulator so that the output voltage of the generator becomes a specified value. Meanwhile, it is required for the generators to still be operable even when the idling rotation speed of an engine is low, the amount of electric loads mounted on a vehicle becomes large, and/or the engine consumes less fuel. These demands are typical for recent engines.
To meet such needs, one conventional control technique is provided by Japanese Patent Publication No. 3070788, in which the output voltage of an on-vehicle AC generator is controlled based on vehicle running states, engine operating states, and battery charged states. More practically, in this control technique, a duty signal whose duty ratio corresponds to a reference voltage is sent from an engine control apparatus (engine ECU (electronic control unit)) to an IC regulator, so that the IC regulator controls the output voltage of the generator to be at the reference voltage.
The recent needs for reducing the fuel consumption during a vehicle running period have required the generator to generate a sufficient power at a minimum fuel consumption by properly controlling the amount of work of the generator in response to vehicle running states and battery charged states. An example is that, when the vehicle is in acceleration, the output voltage of the generator is controlled to lower values (for example, down to a minimum voltage of 12 V) so that the physical load to the engine reduces for lowering the fuel consumption. In contrast, when the vehicle is in deceleration, the output voltage of the generator is controlled to higher values (for example, up to a maximum voltage of 15 V) so that the generated amount from the generator increases for rapidly charging the battery. This permits the inertia energy of the engine to be converted to electric power, thereby effectively making use of the fuel.
In controlling the output voltage of the generator, the ECU transmits to the IC regulator a pulse signal whose cycle (pulse repetition time) is specified and constant. However, for example, different manufactures may produce ECUs of which pulse cycles are different from each other. And it is often required to employ those ECUs as an on-vehicle ECU to transmit a pulse signal to the on-vehicle IC regulator. Thus the IC regulator should have a margin for receiving pulse signals having different cycles. However, noise may be superposed in the pulse signal. In such a case, when the IC regulator has a large amount of the margin for the cycle, the amount of the noise tends to be greater as well, which may cause the IC regulator to erroneously recognize the pulse signal. As a result, the output voltage of the generator may not be controlled properly, thereby resulting in undesired changes in the output voltage.